The present invention relates to the field of polymeric tubes, and particularly to the field of flexible polymeric automobile fuel and vapor transmission tubes which have reduced permeability to fuel and vapor. More particularly, the present invention relates to polybutylene terephthalate (PBT) and polybutylene naphthalate (PBN) tubes and to the use of such tubes to reduce the amount of fuel vapor released to the atmosphere from motor vehicles.
Recent environmental regulations imposed on the automotive industry and on the fuel delivery industries severely limit the amount of fuel vapor that can permeate from the fuel system of motor vehicles and from the fuel delivery hoses used to transport such fuels. It is anticipated that in some states such as California, future federal and state regulation will fix the limit for permissible hydrocarbon emissions at a maximum of 0.5 grams/per vehicle of fuel vapor emission per 24 hours period with the engine not running (S.H.E.D. TEST). Such emissions measured are those vapor emissions permeating from the fuel hose and any other parts of the fuel supply system.
Choosing the right combination of materials used in the construction of fuel transport tubes, such as fuel filler tubes, to provide high performance, long service life, and low permeability of fuel and vapor in the tube, while maintaining manufacturing costs at an acceptable level, has been more difficult than ever before.
Various types of tubing have been proposed to address these concerns. In general, the most successful tubes have been co-extruded multi-layer tubes which employ a relatively thick outer layer composed of a material which is resistant to the external environment while the inner layer is generally thinner and is composed of a material which is chosen for its ability to prevent permeation of fuel liquid and vapor.
Typically, fuel transfer hoses, in the past, have been constructed of natural or synthetic rubber material such as butadiene-acrylonitrile rubber or the like. Other hoses have been constructed using a fluoroelastomer as an inner wall surface layer of the hose and some other material as the outer layer. Such hoses have a high permeability to fuel vapor. Attempts to produce fuel transport hoses with reduced permeability to fuel vapors have included the use of corrugated polyamide and fluorocarbon thermoplastic tubes. However, these structures are presently considered to be only marginally effective to reduce the permeability of fuel vapors while being relatively expensive.
Other attempts to produce a fuel tube with reduced permeability to fuel vapors use a tetrafluoroethylene-hexafluoropropylene-vinylidine fluoride terpolymer liner and a layer of hexafluoropropylene-vinylidine fluoride copolymer or other suitable elastomer as the conductive inner part of the tube. For example, such hoses are discussed in U.S. Pat. No. 4,606,952 to Sugimoto and U.S. Pat. No. 5,430,603 to Albino et al. Such hose structures, though, have a tendency to wrinkle on the inner radius of the forming mandrel or pin causing an undesirable and discernable defect which may also exhibit a weakened area in the hose.
Polybutylene terephthalate has been used as a thin barrier layer in multilayer hoses or tubes as disclosed in U.S. Pat. Nos. 5,996,642; 5,910,544; and 5,474,109. Other examples of prior art patents which teach multilayer polymer hoses or tubes containing polybutylene terephthalate in one of the layers include U.S. Pat. No. 6,192,942 to Hsich et al. which teaches a multi-layer assembly for use in fuel line applications, wherein the multiphase polymer may be polybutylene terephthalate and U.S. Pat. No. 6,179,008 to Kawazura, et al. which teaches rubber hoses composed of an inner tube of polybutylene terephthalate.
It is clear that there have been many problems and many proposed solutions to said problems. However, there remains an urgent need, particularly in the automotive and fuel delivery industries for a fuel hose which prevents permeation of fuels and vapor and which resists delamination under stress over long periods of time while maintaining manufacturing costs at an acceptable level.
The present invention provides fuel tubes for use in fuel systems which not only drastically reduces or prevents permeation of fuel vapor into the environment but also eliminates the problem of delamination of the various layers of materials, particularly barrier materials such as PVDF, THV, PTFE, ETFE, etc. used in the construction of such tubes. Since the permeation rate of fuel vapor through a hose wall is inversely proportional to the thickness of the hose wall, it has been found that certain materials having sufficient barrier properties can be used to form the hose wall without the need for a separate barrier layer. However, such material must also be flexible, possess superior strength and durability, and be resistant to degradation by the fuel.
In accordance with the present invention, polyalkylene terephthalate or polyalkylene naphthalate, and preferably a polyalkylene terephthalate, or polyalkylene naphthalate in which the alkylene component contains 1 to about 6 carbon atoms, has the above characteristics. In a preferred aspect of the invention the polyalkylene terephthalate is polybutylene terephthalate (PBT) and the polyalkylene napthalate is polybutylene napthalate (PBN). The invention particularly relates to fuel transport hoses, wherein polybutylene terephthalate or polybutylene naphthalate is employed throughout the entire wall of the hose to provide reduced permeability without the need for a separate barrier layer. Typically, the polybutylene terephthalate or or polybutylene naphthalate hose of the present invention exhibits a fuel liquid and vapor permeation of less than about 1 g/m2/day of CE-10 at 40xc2x0 C. In addition to reduced permeability, the hose of the present invention has adequate strength and durability over long periods of time, and is resistant to chemical degradation by the fluids being transported therein.
Polybutylene terephthalate is a relatively stiff material, but is considered adequate for the purpose of this invention. In certain situations where more flexibility is desired, the polybutylene terephthalate can be built having a corrugated structure which allows additional flexibility depending upon the extent and degree of the corrugation and upon the particular use of the hose.
Typically, fuel transport hoses require that at least the inner surface of the hose is conductive to dissipate any static buildup that may occur. Accordingly, the polybutylene terephthalate may contain a conductive agent in an amount to prevent static discharge. Typically, the conductive agent is carbon black, but may be any conductive agent or combination of conductive agents commonly recognized in the industry to provide conductivity to a rubber or plastic material.